This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 2000-225708 filed on Jul. 26, 2000, the entire content of which is incorporated herein by reference.
1. Field of Invention
The present invention is generally directed to vehicle seat. More particularly, the present invention pertains to a seat recliner for a vehicle that is capable of desirably adjusting and maintaining a tilted angle between the seat back and the seat cushion of a vehicle seat.
2. Background of the Invention
A known seat recliner for a vehicle is disclosed in a Japanese Patent Application published on Sep. 9, 1997 as Toku-Kai-Hei 9 (1997)-234132. This vehicle seat recliner has a lower arm fixed to a seat cushion, an upper arm fixed to a seat back and rotatably supported by the lower arm, a pawl slidably movable in the lower arm, an inner gear portion formed on the upper arm for engaging the pawl, and a pressure plate rotatably supported by the lower arm and urging the pawl into engagement with the inner gear portion.
The backside of the pawl is provided with a cam surface and a projecting portion on the pressure plate contacts the cam surface. The pressure plate further has a first contact portion and a second contact portion formed on both sides of the projecting portion.
The pawl is urged by engaging the cam surface with the projecting portion so that the pawl engages the inner gear portion of the upper arm. Then the engagement between the pawl and the inner gear portion regulates the upper arm not to rotate relative to the lower arm, thereby maintaining any desired tilted angle between the seat back and the seat cushion of the vehicle seat. When the pressure plate is rotated, the contact between the cam surface and the pressure plate is released, and the pawl is also slidably moved toward the pressure plate, whereby the engagement between the pawl and the inner gear portion is released. Then, the rotation of the upper arm relative to the lower arm is permitted so that the tilt angle between the seat back and the seat cushion can be adjusted. The first contact portion or the second contact portion of the pressure plate is designed to contact the back side of the pawl only when the upper arm is given an excessive load while the upper arm is regulated not to rotate relative to the lower arm.
The contact with the backside of the pawl prevents the pawl from inclining relative to the lower arm and so undesired disengagement of the pawl from the inner gear portion is prevented. However, due to small gaps between the contact portions of the pressure plate and the backside of the pawl, a slight incline of the pawl inevitably occurs till the pawl backside touches on the first contact portion or the second contact portion. The inclination of the pawl to one direction causes an increase of the pressure angle of the cam surface against the projection of the pressure plate because the cam surface is formed on the pawl for urging the pawl. This increase of the pressure angle causes the pushing force applied to the pawl to be decreased. The possibility of undesirable disengagement of the pawl from the inner gear portion thus still remains.
To restrict the inclination of the pawl and prevent an increase of the pressure angle of the cam, tight contact of the backside of the pawl with the first and second contact portions might have some effect. However, to achieve such tight contact, a relatively highly precise formation of the backside of the pawl and each of the first and second contact portions is necessary. This precise formation undesirably decreases the productivity. Also, such tight engagement of the backside of the pawl with the first and second contact portions can have adverse effects in other regards such as with respect to operation feeling.
Accordingly, a need exists for an improved seat recliner for a vehicle that is not as susceptible to the disadvantages and drawbacks discussed above.
It would be desirable to provide a seat recliner for a vehicle which can relatively reliably prevent disengagement between the pawl and the inner gear portion formed in the upper arm.
In accordance with one aspect of the invention, a seat recliner for a vehicle includes a lower arm adapted to be fixed with respect to a seat cushion, an upper arm adapted to be fixed with respect to a seat back and rotatably supported by the lower arm, an inner gear portion formed at the upper arm, a pawl slidably supported by the lower arm and engageable with the inner gear portion, a pressure member rotatably supported by the lower arm to urge the pawl into engagement with the inner gear portion, a projecting portion formed on a back surface of the pawl for engagement with the pressure member, a cam surface formed on the pressure member for engagement with the projecting portion, a first contact portion formed on one side of the cam surface of the pressure member for contacting the back surface of the pawl, and a second contact portion formed on an opposite side of the cam surface of the pressure member for contacting the back surface of the pawl.
Thus, the seat recliner is designed so that the cam surface is formed on the pressure member, and the first and second contact portions are formed on the pressure member. When the upper arm receives an excessive load, inclination of the pawl is restricted to an extent defined by the gap between the first contact portion or the second contact portion and the cam surface of the pressure member. Although a slight inclination of the pawl occurs, this inclination does not increase the pressure angle of the cam surface, thus preventing undesirable disengagement between the pawl and the inner gear portion of the upper arm. Additionally, by virtue of the gaps between the backside of the pawl and each of the first and second contact portions, precise forming of the various parts is not needed, thus increasing the productivity and facilitating the manufacture of the seat recliner.
In accordance with another aspect of the invention, a seat recliner for a vehicle includes a lower arm adapted to be fixed with respect to a seat cushion, a shaft supported for rotation on the lower arm, an upper arm adapted to be fixed with respect to a seat back and rotatably supported on the shaft for rotation relative to the lower arm, an inner gear portion formed at the upper arm, a pawl supported by the lower arm and slidably movable into engagement with the inner gear portion to restrict rotation of the upper arm relative to the lower arm and out of engagement with the inner gear portion to permit rotation of the upper arm relative to the lower arm, the pawl including a back side from which extends a projecting portion, and a cam supported on the shaft for rotation together with the shaft about a rotational axis. The cam has a cam surface positioned in opposing relation to the projecting portion of the pawl to engage the projecting portion and urge the pawl into engagement with the inner gear portion. A projecting contact surface is provided on the cam, is positioned on one side of the cam surface and is spaced from the cam surface for being contacted by a back surface of the pawl when the pawl is inclined during application of a load to the upper arm.